Looks like it will drop to about half the current surface temperature as it expands (although this seems to be talking about it at around 0.5 AU) http://www.astronomy.ohio-state.edu/~ryden/ast162_4/notes15....
On the one hand, artists’ conceptions of boiled oceans and cities in cinders that saddened and discouraged me in my childhood. On the other hand, the heat energy density of Sol today is comparable to a compost heap. When the radius of a sphere doubles, it’s volume increase eight times.
If Sol is too itsy to start helium fusion, maybe orbiting within the post-expansion photosphere - the hydrogen envelope - is chill, damp, and sparky?